Yet Danes are almost defiantly merry. Not only did their country rank No. 1 in both the 2013 U.N. World Happiness Report (WHR) and the inaugural 2012 edition, but it has topped the European Commission's well-being and happiness index for 40 years in a row.

So what's behind all this boreal bliss? It's partly a regional phenomenon, since the U.N. also lists Scandinavian neighbors Norway and Sweden among its five happiest countries, along with nearby Switzerland and the Netherlands. But Denmark stands out even in euphoric Northern Europe, suggesting the country has an emotional ace up its sleeve.

But beyond all that, Denmark endures dreary winters with the help of an arcane cultural concept known as "hygge." It's not an easy word for outsiders to pronounce — it sounds sort of like HYU-gah — and it's even harder to translate. Hygge apparently has no direct analogue in English, and related words like "coziness," "togetherness" and "well-being" only cover a fraction of its nebulous definition. Still, in hopes of shedding light on Denmark's world-class happiness, here's a closer look at the hazy nature of hygge.

Hygge, originally a Norwegian word for "well-being," first appeared in Danish near the end of the 18th century, according to Denmark's tourism bureau. It has evolved into a big part of Danish life since then, absorbing connotations over time like a semantic snowball. The dark winters of Denmark helped turn hygge from a mere word into a kind of cultural panacea, manifested in various ways to buffer Danes against cold, solitude and stress.

"In other languages the word for hygge or coziness is more a physical thing, and hygge is more a mental thing," explains Lotte Hansen, a library science student from Aalborg, Denmark, who's interning at the Museum of Danish America in Elk Horn, Iowa. "It's like a feeling, and it's big at Christmastime. The candles, the food, being with your family."

"It's not only Christmas, though," she adds, noting hygge is a pervasive, year-round spirit. "It's like a mood you have. We can see hygge in many things, in many situations."

This flexibility of hygge is a major reason why English words like "cozy" don't do it justice. "Coziness relates to physical surroundings — a jersey can be cozy, or a warm bed — whereas hygge has more to do with people's behavior toward each other," writes author Helen Dyrbye in "Xenophobe's Guide to the Danes." "It is the art of creating intimacy: a sense of comradeship, conviviality and contentment rolled into one."

Danes don't have a monopoly on these concepts, but they do take pride in their holistic way of looking at them. It's not unlike the American idea of thankfulness around Thanksgiving and Christmas, which refers to a general sense of gratitude as well as the implied presence of family, festivity and homemade food. Yet while holiday cheer doesn't last all year for many Americans — despite its potential health benefits — hygge has become embedded in the Danish consciousness.

"My feeling is that American life is so rushed that we often forget about doing things and creating these events of hygge," says Michele McNabb, librarian for the Museum of Danish America. "Americans vary so much in their family connections and friend networks, but you have to slow down for it. Hygge is not something you can do in a rush."

The word is useful as a noun or a verb, McNabb adds — "you can hygge by curling up on the sofa with a good book" — and as an adjective by converting it to "hyggeligt" (HYU-gah-lee). It generally has a social component, but there are wide-ranging interpretations across Denmark, allowing it to describe anything from a person or a building to an abstract ambience or sentiment. And for Danes who travel or move to America, the lack of a clear English translation can feel linguistically limiting.

"It's often connected to some social thing, but also a house can be hyggeligt, or different places can be hyggeligt," says Hansen, who came to the U.S. from Denmark just a few months ago. "We use it really often. When I came over here, I had to take a moment to think, 'What word can I use to describe this when I can't use hygge?'"

Of course, it's hard to pinpoint how much hygge fuels Danish happiness, but as the U.N.'s WHR points out, mental health and social support are known to affect national well-being. "Mental health is the biggest single factor affecting happiness in any country," Columbia University's Earth Institute reported after the first WHR release in 2012, adding that "stable family life and enduring marriages are important for the happiness of parents and children." And while happier countries tend to be rich, it noted, "more important for happiness than income are social factors like the strength of social support."

If Denmark's happiness really is a product of hygge, as the country's tourism website suggests, maybe it could be exported to less jubilant nations? The U.S. ranks No. 17 globally in the 2013 WHR — behind both Canada and Mexico, as well as Panama — but perhaps an extra dose of hygge could lift American spirits a bit?

"I think it should be universally adapted," McNabb says. "I'm sure in other cultures there are some things that are similar. I just think the busier our lives get and the more on-call we are 24/7, there's a tendency to overdo things and be overstressed. The concept of carving time out for simple things is very important."